WRW

Tuesday, May 29, 2012

REELING IT IN Think about winding up a garden hose. When it fails to guide evenly, it builds up on one side of the reel, coils too loosely, tangles, jams or kinks. Super frustrating. That's exactly the type of problem Bell Plastics — a mandrel manufacturer — had to deal with in its original guidance mechanism.

"It simply wasn't providing adequate control and this presented us with a number of problems," Bell Plastics Production Engineer Sean Noonan told Process and Control Today in a March article. "The mandrel tended to stack in one place as it wound, rather than being layered evenly — often these stacks would build up and then collapse, leaving tangled loose coils on the drum."

THE CHALLENGE That type of jamming could damage the mandrel, Noonan explained. And once it's damaged, it has to get scrapped. Plus, the rewind process dramatically slows production because the operator has to untangle the mandrel by hand.

"This meant a job that should take maybe three hours could day days," Noonan said. "Also, the snatching and snagging as the tangles jammed during rewind would often mark the mandrel. Indeed, sometimes the mandrel would be so badly tangled, it would have to be cut from the winder and scrapped."

Basically, the whole process needed a motion control makeover.

THE SOLUTION Enter, the PDU2M HepcoMotion Profile Driven Unit. Bell Plastics designed a PDU2M to the front of each winder to carry the guides that the mandrel passes through. Since every one of the system's mandrels are extruded, the PDU2M moves back and forth to evenly guide the mandrel onto the winder drums and make sure it's coiled evenly across the width of it.

Hoses are usually made up of several layers, typically of rubber or plastic sheets, textile or alloy reinforcement. The manufacturer makes the host by layering one of those materials onto a mandrel to give the hose its shape. The mandrel basically creates the hole down the middle that runs the length of the hose. Then, the composite gets vulcanized, which helps melds the layers together. Then, it's unwound from the mandrel to make way for the next hose.

ROOM TO FLEX Bell Plastics specializes in flexible mandrels, according to Process and Control Today. Manufacturers used to use super rigid mandrels like steel rods, but one of the downsides was the length limitations on the end product. These days, most hose-makers use flexible mandrels made up of a variety of materials and in super long lengths — some up to several miles. In the end, it gets packed in tighter, easy-to-handle coils.

Bell Plastics was among the first in its industry to switch to flexible mandrels like that. It developed a unique way to make them free from holes and and air pockets, which could make the mandrel collapse during hose manufacturing.

IMPROVING THE PROCESS The HepcoMotion PDU2M helped Bell Plastics improve the whole process because the actuators automatically adjusted the travel pace based on the the mandrel size and line speed. The operator uses a touch screen to adjust the settings for every production run.

"There is provision in the control unit for future integration with an automated control system, so that selecting the parameters for a particular product on the extruder will automatically set up the PDU2M control," said Noonan, quoted in Process and Control Today. "We have also taken the opportunity to improve the way the mandrel is guided along the whole of the production line, reducing the risk of scrap generation."

What Bell Plastics wanted most out of the linear motion system was that it would be able to guide all the mandrels and adjust to shifting forces. Hepco's profile driven unit worked well for this application because its external carriage guides are built into the unit, Noonan explained. Plus, the unit would tolerate mounting on one of the existing system's stock bright steel plates, he added.

A competitor's product, for example, would have had the carriages run on another guide rail mounted onto a machined surface that would have to be exactly aligned with the guide — that means extra cash for extra build costs, Noonan said.

LIGHTS OUT The PDU2M doubled the moment load capacity and increased the uplift in moment load stiffness by 1,000 percent. Direct load capacity upped by 50 percent. The stability and consistency of the PDU2M automated system gave Bell Plastics the ability to run lights-out production without fear of any problems resulting from having to manually winding the mandrels.

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